WaffleGuy
Colony
You can win 4.1 without actually killing all amphibians in the final wave, but only two minutes after it has started.
Basically, or as far as I know, two minutes after the wave starts (three minutes after the bullfrog is gone), the game will check if there are any active underground predators. If there aren't, you win. This can be exploited by simply fighting all the amphibians outside, and when the two minutes pass and the game starts to check, you'll just win. Even if one amphibian gets in, if you can kill it before any others do, you'll still win.
Basically, or as far as I know, two minutes after the wave starts (three minutes after the bullfrog is gone), the game will check if there are any active underground predators. If there aren't, you win. This can be exploited by simply fighting all the amphibians outside, and when the two minutes pass and the game starts to check, you'll just win. Even if one amphibian gets in, if you can kill it before any others do, you'll still win.